Obesity and diabetes are more common in African-Americans than whites. Because free fatty acids (FFA) participate in the development of these conditions, studying race differences in the regulation of FFA and glucose by insulin is essential. Background: Quantitative evaluation of insulin regulation on plasma glucose and free fatty acid (FFA) in response to external glucose challenge is clinically important to assess the development of insulin resistance. Mathematical minimal models (MMs) based on insulin modified frequently-sampled intravenous glucose tolerance tests (IM-FSIGT) are widely applied to ascertain an insulin sensitivity index. However, the action of insulin on FFA kinetics is not considered in most MMs. Neither glucose clamps nor IM-FSIGT are normal physiological conditions so it is important to quantify insulin modulation of glucose and FFA metabolism in postprandial state. Our contribution in this collaboration is in assessing post-prandial insulin secretion rate and insulin clearance in Dr. Sumner's Federal Womens cohort. We are also working with Dr. Sumner's group in analyzing Vitamin D levels in connection with bone density and thyroid hormone.